1. Field of the Invention
The present invention is directed to a blow-needle assembly for cooling a blow-molded article with a liquid. More specifically, the present invention is directed to a blow-molding needle that pierces a plastic parison and forms a fluid tight seal between the needle and mold surface by compressing the plastic parison between the blowing needle and an aperture in the mold.
2. Description of the Related Art
U.S. Pat. No. 3,937,610 ('610) teaches a method of cooling the interior of a blow molded article with a liquid mist. The '610 patent is directed to a method for reducing the cycle time of molding a blown article by reducing the time needed to cool the article before it can be removed from the mold. After the article is blown, small globules of liquid are circulated through the interior of the article. The liquid evaporates when it contacts the hot plastic wall, thus reducing the temperature of the blown article. Air is circulated within the article to evaporate any remaining liquid. A volume of cooling liquid is not circulated within the interior of the article. Only small liquid globules suspended within the mist contact the article walls. While the method described in the '610 patent reduces the time needed to cool the article, the cycle time reduction is not as great as in the present invention. The liquid globules suspended within the mist do not have sufficient capacity to rapidly cool thick-walled blow molded articles when compared to a solid liquid medium.
Two additional references which also teach including liquid within the blowing medium are U.S. Pat. No. 5,498,390 and Japanese Patent Application No. 05-023094. These references similarly require that the cooling liquid be suspended within the blowing medium and evaporate upon contact with the hot parison walls. While this method of manufacturing blow molded articles reduces the cycle time when compared with ambient cooling, it does not provide the rapid cooling of the present invention due to the superior ability of liquid water to remove heat energy.
Japanese Patent Application No. 05-104616 ('616) teaches a method of making a container by blow molding. After the container has been blow molded, a cooling liquid is introduced into the interior of the molded article. This is known as "water casting" where a quantity of cooling liquid equal to the volume of the container is introduced and held within the article. The amount of heat removed from the article is limited by the volume of water. In the present invention, the cooling liquid is circulated through the article and more than the container volume of cooling liquid may be circulated through the article to remove more heat. The present invention also introduces a constant "in-out" flow of water, creating turbulence. Turbulent flow inside the article provides the greater thermal cooling.
The '616 patent application teaches a method of molding a container around a blowing mandrel. The parison seals between the outer perimeter of the water inlet and the mold to form a fluid-tight seal. Sealing between the parison and the water inlet system has been a key impediment for using liquid cooling for blow molding. Most mold applications do not support the use of a mandrel between the mold walls. In these applications, needle or pin is used to pierce the parison and inject cooling liquid into the molded article. Forming a fluid-tight seal between the parison and the needle is necessary to implement liquid cooling.
U.S. Pat. No. 5,565,165, ('165) teaches a blow-molding apparatus having two blow needles, one having a larger diameter and the other having a smaller diameter. The smaller diameter needle is used to inflate the parison and hold the parison against the mold surface while the larger diameter needle pierces the parison. The larger diameter needle is capable for ventilating the interior portion of the article with a larger quantity of cooling fluid. The small and large diameter needles have a tip, small diameter shank, large diameter shank and tapered portion between the large diameter shank.
U.S. Pat. No. 5,759,475 ('475), teaches a blow-molding needle having blowing inlets positioned slightly behind the needle tip. This enables the blowing inlets to be constructed of a larger diameter than if they had passed through the needle tip.
Neither the '165 patent nor the '475 patent are directed to a blow-molding apparatus that cools the interior surface of a molded article with a liquid. Both use a gas to cool the parison. The needle tapered portions do not appear to contact the parison wall during the inflation process and do not act as a fluid-tight sealing surface.
The present invention is useful for applications where a fluid tight seal is required between the blowing needle and the mold surface. These and other disadvantages of the prior art are overcome by the method taught in the present invention.